Although the proliferation of digital communications equipment has met with widespread acceptance in a variety of industries, telephone companies have been slow to convert to or integrate digital signalling subsystems and communication schemes into their well established copper wire networks. One of the principal reasons for such reticence is the fact that a significant part, if not all, of an established telephone network employs analog signalling equipment. Still, because of substantial user demand, regional Bell operating companies (RBOC's) currently provide leased-line digital services to sophisticated customers, who maintain their (digital) communications networks with intelligent management systems that provide detailed information regarding the quality of the service being delivered. This information provides the customer with the ability to develop long term statistics for error-free seconds, severely errored seconds, as well as channel availability--i.e. quantitative measures of the quality of service being leased to the customer.
Unfortunately, the network topographies and operating schemes currently embedded in the RBOC's networks do not provide adequate information about the performance of the (digital) service access metallic loops between the serving central office and the network interface at the customer's premises. As a consequence, an RBOC is not readily prepared to deal with a customer who, based upon the customer's own analysis of the data traffic, alleges that the published digital services specifications are not being fulfilled. In addition, the local telephone company also lacks the information needed to observe the success of its own objectives toward delivering the services and means to rapidly detect and respond to degradation or outage in service.
Because of these recognized shortcomings, the RBOC's (and the Telco's in general) are seeking to upgrade the diagnostic tools currently employed for their digital carrier links to schemes that will provide them with the ability to monitor the performance of their metallic loops. Although complete system replacement is one straightforward approach, the service providers generally prefer add-ons or enhancements to already installed systems, in order to allow the bulk of the existing equipment to be preserved and to minimize service interruption when upgrading the network.